1. Field of the Invention
The present invention relates to a liquid droplet jetting apparatus for jetting liquid droplets.
2. Description of the Related Art
In general, an ink-jet printer, which records images, letters or the like on a recording medium such as the printing paper, comprises an ink-jet head (liquid droplet jetting head) which has nozzles for jetting liquid droplets of the ink, and an ink cartridge (liquid storage container, ink tank) for storing the ink to be used for the ink-jet head. Usually, the ink-jet head and the ink cartridge are connected to one another by means of a tube made of resin. The ink, which is stored in the ink cartridge, is supplied to the ink-jet head via the tube.
In recent years, it is investigated that a plurality of ink-jet heads, which jet an ink of the same type (same color), are provided in one printer, for example, in order to improve the recording speed. However, when a plurality of ink cartridges are provided in the printer corresponding to the plurality of ink-jet heads respectively, then the number of the ink cartridges is increased, the cost is increased, and the printer is large-sized. Therefore, it is preferable that the ink can be simultaneously supplied from one ink cartridge to the plurality of ink-jet heads.
Japanese Patent Application Laid-open No. 10-95129 discloses an ink cartridge provided with two ink supply ports. The two ink supply ports of the ink cartridge are connected in parallel to two ink-jet heads by means of two supply tubes (tubes). Therefore, it is possible to supply the ink of the same color to the two ink-jet heads respectively.
When one ink cartridge is connected to two ink-jet heads individually (in parallel) by means of a plurality of tubes, the total length of the tubes is consequently long as compared with a case in which one ink cartridge and two ink-jet heads are connected in series, which results in the increase in the cost. When the tubes are made of resin, and the tubes have the gas permeability to some extent, then the following problem arises. That is, the ink contained in the tubes is dried little by little, and the viscosity is increased (increase in viscosity), and/or the air bubbles make invasion into the tubes from the outside of the tubes. As described above, the ink containing a large amount of air bubbles and the viscosity-increased ink generated in the tubes bring about a large factor to cause the jetting failure in the nozzle. Therefore, when the total length of the tubes is increased as a result of the connection of the ink cartridge and the two ink-jet heads in parallel, then the amount of the ink subjected to the increase in viscosity in the tubes is increased, and/or the amount of air bubbles to make invasion into the tubes is increased. The jetting failure of the nozzle is frequently caused. In view of the above, the present inventors have investigated that one ink cartridge and two ink-jet heads are connected in series in order to shorten the total length of the tubes.
However, when one ink cartridge and two ink-jet heads are connected in series, the length of the tubes is increased for the ink to pass therethrough until arrival at one head of the heads from the ink cartridge in relation to the one head which is separated or disposed far from the ink cartridge and which is positioned on the more downstream side in the ink supply direction. Therefore, the viscosity-increased ink and/or the ink containing a large amount of bubbles is/are apt to be supplied to the one head which is disposed far from the ink cartridge. In other words, the jetting failure tends to arise in the nozzle of the one head which is separated far from the ink cartridge. It is necessary to frequently perform the recovery operation (restoring operation) for recovering the jetting performance in order to remove impurities such as the viscosity-increased ink and the air bubbles, the recovery operation including the purge operation for forcibly discharging the ink from the nozzle.